When dueling in diablo 2, I see a lot of paladins talking about "clagging." How is "clagging" done in diablo 2? And why does it work?
"Clagging" refers to a glitch called "charge lagging".
What happens is this:
A Paladin moves a few screens away, turns on Vigor aura, and then uses Charge to move very fast. This causes your character not to sync properly with the game/server, because the character is moving faster then the server can update. This results in the Paladin seemingly jump/teleport (without the Teleport skill or Enigma Runeword) from place to place.
While the Paladin is desynced from the server, they can also cast Blessed hammers that are invisible to other players and/or not appear where they seem to be (the Paladin's position is not updated correctly for other players. E.g., The Paladin is actually behind a wall, but seems to be in front of your character, you shoot at him the hit animation happens but the Paladin loses no life), giving the Paladin an unfair advantage.
There is a similar glitch with Barbarians and the Increase Speed and Frenzy skill.
See it in action.